1. Field of the Invention
The present invention relates to a medical X-ray imaging apparatus for taking tomograms along desired tomographic planes of subjects, such as the head, body, and hands and legs of a human body.
2. Description of the Related Art
As related arts, Japanese Laid-open Patent Application No. Sho 61-22841 and Utility Model Registration Publication No. Hei 4-48169 disclose an X-ray imaging apparatus for performing TDI (Time Delay Integration) of an image signal by changing the frequency of a charge transfer clock signal in accordance with the movement of an X-ray image formed on a CCD sensor while being moved.
In addition, Japanese Laid-open Patent Application No. Sho 62-43990 discloses a method and an apparatus for X-ray imaging by scanning a charge pattern corresponding to X-ray intensity distribution in a space by using an electrometer after X-ray imaging, wherein artifacts (artificial images) are reduced by correcting the X-ray image.
However, in the above-mentioned related arts, when dark current noise, variations in sensitivity, etc. occur in the CCD sensor, artificial images are generated in the X-ray image taken by an X-ray imaging apparatus, causing not only reduction in image quality and resolution but also the danger of erroneous diagnosis. Furthermore, since numerous light-receiving pixels are formed on the CCD sensor, the manufacturing yield of such CCD sensors is lowered extremely when an attempt is made to obtain CCD sensors having small variations in performance, eventually resulting in higher cost.
Furthermore, in Japanese Laid-open Patent Application No. Sho 62-43990, signal processing different from that of the TDI method is performed by using a special X-ray imaging device referred to as an X-ray converting photoconductor made selenium. It is therefore considerably difficult to directly apply the image correction method used for the special signal processing to the TDI method.